Currently in 3GPP (Third Generation Partnership Project), standardization of a 4G wireless communication system (cellular system) is under way. In such a wireless communication system, it is important to improve communication capacity at a cell edge. Thus, CoMP (Coordinated Multi-Point) is under discussion as a means for improving communication capacity at a cell edge.
CoMP is a method of performing communication with user terminals in which a plurality of base stations cooperatively controls transmission/reception parameters, scheduling, or beam/antenna directivity. Effects such as stabilization of communication quality and increased communication capacities are expected from CoMP.
In a wireless communication system, it is also important to efficiently support communication traffic that arises locally. From the above perspective, the introduction of HetNet (Heterogeneous Network) is also under discussion. HetNet is a network in which large and small cells are arranged like being overlaid. According to HetNet, communication capacities in the whole area can be improved by communication traffic that arises locally, which has been hard to be covered by a large cell like a macro sell, being covered by a small cell. As base stations forming each cell, eNodeB, an RRH (Remote RadioHead) cell base station, a hot zone base station (Pico/micro cell eNB), a femto cell base station (Home eNB), and a relay apparatus (relay base station) can be assumed.
These base stations can roughly be divided into CSG (Closed Subscriber Group) cells that have access restrictions of user terminals and OSG (Open Subscriber Group) that have no access restrictions. For example, a femto cell base station is considered for operation as a CSG cell in the home and a preset user terminal can access the femto cell base station. Technology in consideration of such a CSG cell is disclosed by, for example, Patent Literature 1 and Patent Literature 2.